Limosilactobacillus reuteri 3613-1 Delays Onset of Unconfirmed Urinary Tract Infections in Otherwise Healthy Women

Urinary tract infections (UTIs) impose a substantial burden on women’s health, and probiotics have emerged as an alternative strategy to support urogenital wellbeing. This study evaluated the antimicrobial properties of Limosilactobacillus reuteri 3613-1 and its ability to improve UTI outcomes in women with a history of recurrent uncomplicated UTIs. In vitro assays demonstrated that L. reuteri 3613-1 inhibited the growth of Escherichia coli isolates and proved superior inhibition of Gardnerella vaginalis and Candida albicans compared with a comparator L. reuteri strain, supported by confirmed reuterin production and genomic profiling. A randomized, double-blind, placebo-controlled clinical trial (n = 130) assessed daily supplementation with L. reuteri 3613-1 for 24 weeks. While the proportion, frequency, and intensity of confirmed UTIs did not differ significantly between groups, L. reuteri 3613-1 delayed the onset of the first UTI, reaching significance in participants with suspected while unconfirmed UTIs. Vaginal pH and vaginal microbiome composition remained stable and comparable between groups across the intervention. The product was safe and well tolerated. Overall, L. reuteri 3613-1 shows promise as a probiotic candidate with antimicrobial activity and potential to delay symptom onset in women susceptible to recurrent UTIs, warranting further investigation in larger studies.